| .\" -*- nroff -*- |
| .\" |
| .\" sshd.8.in |
| .\" |
| .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
| .\" |
| .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| .\" All rights reserved |
| .\" |
| .\" Created: Sat Apr 22 21:55:14 1995 ylo |
| .\" |
| .\" $Id: sshd.8,v 1.6 1999/11/11 06:57:40 damien Exp $ |
| .\" |
| .Dd September 25, 1999 |
| .Dt SSHD 8 |
| .Os |
| .Sh NAME |
| .Nm sshd |
| .Nd secure shell daemon |
| .Sh SYNOPSIS |
| .Nm sshd |
| .Op Fl diq |
| .Op Fl b Ar bits |
| .Op Fl f Ar config_file |
| .Op Fl g Ar login_grace_time |
| .Op Fl h Ar host_key_file |
| .Op Fl k Ar key_gen_time |
| .Op Fl p Ar port |
| .Sh DESCRIPTION |
| .Nm |
| (Secure Shell Daemon) is the daemon program for |
| .Xr ssh 1 . |
| Together these programs replace rlogin and rsh programs, and |
| provide secure encrypted communications between two untrusted hosts |
| over an insecure network. The programs are intended to be as easy to |
| install and use as possible. |
| .Pp |
| .Nm |
| is the daemon that listens for connections from clients. It is |
| normally started at boot from |
| .Pa /etc/rc . |
| It forks a new |
| daemon for each incoming connection. The forked daemons handle |
| key exchange, encryption, authentication, command execution, |
| and data exchange. |
| .Pp |
| .Nm |
| works as follows. Each host has a host-specific RSA key |
| (normally 1024 bits) used to identify the host. Additionally, when |
| the daemon starts, it generates a server RSA key (normally 768 bits). |
| This key is normally regenerated every hour if it has been used, and |
| is never stored on disk. |
| .Pp |
| Whenever a client connects the daemon, the daemon sends its host |
| and server public keys to the client. The client compares the |
| host key against its own database to verify that it has not changed. |
| The client then generates a 256 bit random number. It encrypts this |
| random number using both the host key and the server key, and sends |
| the encrypted number to the server. Both sides then start to use this |
| random number as a session key which is used to encrypt all further |
| communications in the session. The rest of the session is encrypted |
| using a conventional cipher, currently Blowfish and 3DES, with 3DES |
| being is used by default. The client selects the encryption algorithm |
| to use from those offered by the server. |
| .Pp |
| Next, the server and the client enter an authentication dialog. The |
| client tries to authenticate itself using |
| .Pa .rhosts |
| authentication, |
| .Pa .rhosts |
| authentication combined with RSA host |
| authentication, RSA challenge-response authentication, or password |
| based authentication. |
| .Pp |
| Rhosts authentication is normally disabled |
| because it is fundamentally insecure, but can be enabled in the server |
| configuration file if desired. System security is not improved unless |
| .Xr rshd 8 , |
| .Xr rlogind 8 , |
| .Xr rexecd 8 , |
| and |
| .Xr rexd 8 |
| are disabled (thus completely disabling |
| .Xr rlogin 1 |
| and |
| .Xr rsh 1 |
| into that machine). |
| .Pp |
| If the client successfully authenticates itself, a dialog for |
| preparing the session is entered. At this time the client may request |
| things like allocating a pseudo-tty, forwarding X11 connections, |
| forwarding TCP/IP connections, or forwarding the authentication agent |
| connection over the secure channel. |
| .Pp |
| Finally, the client either requests a shell or execution of a command. |
| The sides then enter session mode. In this mode, either side may send |
| data at any time, and such data is forwarded to/from the shell or |
| command on the server side, and the user terminal in the client side. |
| .Pp |
| When the user program terminates and all forwarded X11 and other |
| connections have been closed, the server sends command exit status to |
| the client, and both sides exit. |
| .Pp |
| .Nm |
| can be configured using command-line options or a configuration |
| file. Command-line options override values specified in the |
| configuration file. |
| .Pp |
| The options are as follows: |
| .Bl -tag -width Ds |
| .It Fl b Ar bits |
| Specifies the number of bits in the server key (default 768). |
| .Pp |
| .It Fl d |
| Debug mode. The server sends verbose debug output to the system |
| log, and does not put itself in the background. The server also will |
| not fork and will only process one connection. This option is only |
| intended for debugging for the server. |
| .It Fl f Ar configuration_file |
| Specifies the name of the configuration file. The default is |
| .Pa /etc/ssh/sshd_config . |
| .Nm |
| refuses to start if there is no configuration file. |
| .It Fl g Ar login_grace_time |
| Gives the grace time for clients to authenticate themselves (default |
| 300 seconds). If the client fails to authenticate the user within |
| this many seconds, the server disconnects and exits. A value of zero |
| indicates no limit. |
| .It Fl h Ar host_key_file |
| Specifies the file from which the host key is read (default |
| .Pa /etc/ssh/ssh_host_key ) . |
| This option must be given if |
| .Nm |
| is not run as root (as the normal |
| host file is normally not readable by anyone but root). |
| .It Fl i |
| Specifies that |
| .Nm |
| is being run from inetd. |
| .Nm |
| is normally not run |
| from inetd because it needs to generate the server key before it can |
| respond to the client, and this may take tens of seconds. Clients |
| would have to wait too long if the key was regenerated every time. |
| However, with small key sizes (e.g. 512) using |
| .Nm |
| from inetd may |
| be feasible. |
| .It Fl k Ar key_gen_time |
| Specifies how often the server key is regenerated (default 3600 |
| seconds, or one hour). The motivation for regenerating the key fairly |
| often is that the key is not stored anywhere, and after about an hour, |
| it becomes impossible to recover the key for decrypting intercepted |
| communications even if the machine is cracked into or physically |
| seized. A value of zero indicates that the key will never be regenerated. |
| .It Fl p Ar port |
| Specifies the port on which the server listens for connections |
| (default 22). |
| .It Fl q |
| Quiet mode. Nothing is sent to the system log. Normally the beginning, |
| authentication, and termination of each connection is logged. |
| .It Fl Q |
| Do not print an error message if RSA support is missing. |
| .El |
| .Sh CONFIGURATION FILE |
| .Nm |
| reads configuration data from |
| .Pa /etc/ssh/sshd_config |
| (or the file specified with |
| .Fl f |
| on the command line). The file |
| contains keyword-value pairs, one per line. Lines starting with |
| .Ql # |
| and empty lines are interpreted as comments. |
| .Pp |
| The following keywords are possible. |
| .Bl -tag -width Ds |
| .It Cm AFSTokenPassing |
| Specifies whether an AFS token may be forwarded to the server. Default is |
| .Dq yes . |
| .It Cm AllowGroups |
| This keyword can be followed by a number of group names, separated |
| by spaces. If specified, login is allowed only for users whose primary |
| group matches one of the patterns. |
| .Ql \&* |
| and |
| .Ql ? |
| can be used as |
| wildcards in the patterns. Only group names are valid, a numerical group |
| id isn't recognized. By default login is allowed regardless of |
| the primary group. |
| .Pp |
| .It Cm AllowUsers |
| This keyword can be followed by a number of user names, separated |
| by spaces. If specified, login is allowed only for users names that |
| match one of the patterns. |
| .Ql \&* |
| and |
| .Ql ? |
| can be used as |
| wildcards in the patterns. Only user names are valid, a numerical user |
| id isn't recognized. By default login is allowed regardless of |
| the user name. |
| .Pp |
| .It Cm CheckMail |
| Specifies whether |
| .Nm |
| should check for new mail for interactive logins. |
| The default is |
| .Dq no . |
| .It Cm DenyGroups |
| This keyword can be followed by a number of group names, separated |
| by spaces. Users whose primary group matches one of the patterns |
| aren't allowed to log in. |
| .Ql \&* |
| and |
| .Ql ? |
| can be used as |
| wildcards in the patterns. Only group names are valid, a numerical group |
| id isn't recognized. By default login is allowed regardless of |
| the primary group. |
| .Pp |
| .It Cm DenyUsers |
| This keyword can be followed by a number of user names, separated |
| by spaces. Login is allowed disallowed for user names that match |
| one of the patterns. |
| .Ql \&* |
| and |
| .Ql ? |
| can be used as |
| wildcards in the patterns. Only user names are valid, a numerical user |
| id isn't recognized. By default login is allowed regardless of |
| the user name. |
| .It Cm HostKey |
| Specifies the file containing the private host key (default |
| .Pa /etc/ssh/ssh_host_key ) . |
| Note that |
| .Nm |
| does not start if this file is group/world-accessible. |
| .It Cm IgnoreRhosts |
| Specifies that rhosts and shosts files will not be used in |
| authentication. |
| .Pa /etc/hosts.equiv |
| and |
| .Pa /etc/ssh/shosts.equiv |
| are still used. The default is |
| .Dq no . |
| .It Cm KeepAlive |
| Specifies whether the system should send keepalive messages to the |
| other side. If they are sent, death of the connection or crash of one |
| of the machines will be properly noticed. However, this means that |
| connections will die if the route is down temporarily, and some people |
| find it annoying. On the other hand, if keepalives are not send, |
| sessions may hang indefinitely on the server, leaving |
| .Dq ghost |
| users and consuming server resources. |
| .Pp |
| The default is |
| .Dq yes |
| (to send keepalives), and the server will notice |
| if the network goes down or the client host reboots. This avoids |
| infinitely hanging sessions. |
| .Pp |
| To disable keepalives, the value should be set to |
| .Dq no |
| in both the server and the client configuration files. |
| .It Cm KerberosAuthentication |
| Specifies whether Kerberos authentication is allowed. This can |
| be in the form of a Kerberos ticket, or if |
| .Cm PasswordAuthentication |
| is yes, the password provided by the user will be validated through |
| the Kerberos KDC. Default is |
| .Dq yes . |
| .It Cm KerberosOrLocalPasswd |
| If set then if password authentication through Kerberos fails then |
| the password will be validated via any additional local mechanism |
| such as |
| .Pa /etc/passwd |
| or SecurID. Default is |
| .Dq yes . |
| .It Cm KerberosTgtPassing |
| Specifies whether a Kerberos TGT may be forwarded to the server. |
| Default is |
| .Dq no , |
| as this only works when the Kerberos KDC is actually an AFS kaserver. |
| .It Cm KerberosTicketCleanup |
| Specifies whether to automatically destroy the user's ticket cache |
| file on logout. Default is |
| .Dq yes . |
| .It Cm KeyRegenerationInterval |
| The server key is automatically regenerated after this many seconds |
| (if it has been used). The purpose of regeneration is to prevent |
| decrypting captured sessions by later breaking into the machine and |
| stealing the keys. The key is never stored anywhere. If the value is |
| 0, the key is never regenerated. The default is 3600 |
| (seconds). |
| .It Cm ListenAddress |
| Specifies what local address |
| .Nm |
| should listen on. |
| The default is to listen to all local addresses. |
| .It Cm LoginGraceTime |
| The server disconnects after this time if the user has not |
| successfully logged in. If the value is 0, there is no time limit. |
| The default is 600 (seconds). |
| .It Cm LogLevel |
| Gives the verbosity level that is used when logging messages from |
| .Nm sshd . |
| The possible values are: |
| QUIET, FATAL, ERROR, INFO, CHAT and DEBUG. |
| The default is INFO. |
| Logging with level DEBUG violates the privacy of users |
| and is not recommended. |
| .It Cm PasswordAuthentication |
| Specifies whether password authentication is allowed. |
| The default is |
| .Dq yes . |
| .It Cm PermitEmptyPasswords |
| When password authentication is allowed, it specifies whether the |
| server allows login to accounts with empty password strings. The default |
| is |
| .Dq yes . |
| .It Cm PermitRootLogin |
| Specifies whether the root can log in using |
| .Xr ssh 1 . |
| The argument must be |
| .Dq yes , |
| .Dq without-password |
| or |
| .Dq no . |
| The default is |
| .Dq yes . |
| If this options is set to |
| .Dq without-password |
| only password authentication is disabled for root. |
| .Pp |
| Root login with RSA authentication when the |
| .Ar command |
| option has been |
| specified will be allowed regardless of the value of this setting |
| (which may be useful for taking remote backups even if root login is |
| normally not allowed). |
| .It Cm Port |
| Specifies the port number that |
| .Nm |
| listens on. The default is 22. |
| .It Cm PrintMotd |
| Specifies whether |
| .Nm |
| should print |
| .Pa /etc/motd |
| when a user logs in interactively. (On some systems it is also |
| printed by the shell, |
| .Pa /etc/profile , |
| or equivalent.) The default is |
| .Dq yes . |
| .It Cm RandomSeed |
| Obsolete. Random number generation uses other techniques. |
| .It Cm RhostsAuthentication |
| Specifies whether authentication using rhosts or /etc/hosts.equiv |
| files is sufficient. Normally, this method should not be permitted |
| because it is insecure. |
| .Cm RhostsRSAAuthentication |
| should be used |
| instead, because it performs RSA-based host authentication in addition |
| to normal rhosts or /etc/hosts.equiv authentication. |
| The default is |
| .Dq no . |
| .It Cm RhostsRSAAuthentication |
| Specifies whether rhosts or /etc/hosts.equiv authentication together |
| with successful RSA host authentication is allowed. The default is |
| .Dq yes . |
| .It Cm RSAAuthentication |
| Specifies whether pure RSA authentication is allowed. The default is |
| .Dq yes . |
| .It Cm ServerKeyBits |
| Defines the number of bits in the server key. The minimum value is |
| 512, and the default is 768. |
| .It Cm SkeyAuthentication |
| Specifies whether |
| .Xr skey 1 |
| authentication is allowed. The default is |
| .Dq yes . |
| Note that s/key authentication is enabled only if |
| .Cm PasswordAuthentication |
| is allowed, too. |
| .It Cm StrictModes |
| Specifies whether |
| .Nm |
| should check file modes and ownership of the |
| user's files and home directory before accepting login. This |
| is normally desirable because novices sometimes accidentally leave their |
| directory or files world-writable. The default is |
| .Dq yes . |
| .It Cm SyslogFacility |
| Gives the facility code that is used when logging messages from |
| .Nm sshd . |
| The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
| LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is AUTH. |
| .It Cm UseLogin |
| Specifies whether |
| .Xr login 1 |
| is used. The default is |
| .Dq no . |
| .It Cm X11Forwarding |
| Specifies whether X11 forwarding is permitted. The default is |
| .Dq yes . |
| Note that disabling X11 forwarding does not improve security in any |
| way, as users can always install their own forwarders. |
| .It Cm X11DisplayOffset |
| Specifies the first display number available for |
| .Nm sshd Ns 's |
| X11 forwarding. This prevents |
| .Nm |
| from interfering with real X11 servers. |
| .El |
| .Sh LOGIN PROCESS |
| When a user successfully logs in, |
| .Nm |
| does the following: |
| .Bl -enum -offset indent |
| .It |
| If the login is on a tty, and no command has been specified, |
| prints last login time and |
| .Pa /etc/motd |
| (unless prevented in the configuration file or by |
| .Pa $HOME/.hushlogin ; |
| see the |
| .Sx FILES |
| section). |
| .It |
| If the login is on a tty, records login time. |
| .It |
| Checks |
| .Pa /etc/nologin ; |
| if it exists, prints contents and quits |
| (unless root). |
| .It |
| Changes to run with normal user privileges. |
| .It |
| Sets up basic environment. |
| .It |
| Reads |
| .Pa $HOME/.ssh/environment |
| if it exists. |
| .It |
| Changes to user's home directory. |
| .It |
| If |
| .Pa $HOME/.ssh/rc |
| exists, runs it; else if |
| .Pa /etc/ssh/sshrc |
| exists, runs |
| it; otherwise runs xauth. The |
| .Dq rc |
| files are given the X11 |
| authentication protocol and cookie in standard input. |
| .It |
| Runs user's shell or command. |
| .El |
| .Sh AUTHORIZED_KEYS FILE FORMAT |
| The |
| .Pa $HOME/.ssh/authorized_keys |
| file lists the RSA keys that are |
| permitted for RSA authentication. Each line of the file contains one |
| key (empty lines and lines starting with a |
| .Ql # |
| are ignored as |
| comments). Each line consists of the following fields, separated by |
| spaces: options, bits, exponent, modulus, comment. The options field |
| is optional; its presence is determined by whether the line starts |
| with a number or not (the option field never starts with a number). |
| The bits, exponent, modulus and comment fields give the RSA key; the |
| comment field is not used for anything (but may be convenient for the |
| user to identify the key). |
| .Pp |
| Note that lines in this file are usually several hundred bytes long |
| (because of the size of the RSA key modulus). You don't want to type |
| them in; instead, copy the |
| .Pa identity.pub |
| file and edit it. |
| .Pp |
| The options (if present) consists of comma-separated option |
| specifications. No spaces are permitted, except within double quotes. |
| The following option specifications are supported: |
| .Bl -tag -width Ds |
| .It Cm from="pattern-list" |
| Specifies that in addition to RSA authentication, the canonical name |
| of the remote host must be present in the comma-separated list of |
| patterns ('*' and '?' serve as wildcards). The list may also contain |
| patterns negated by prefixing them with '!'; if the canonical host |
| name matches a negated pattern, the key is not accepted. The purpose |
| of this option is to optionally increase security: RSA authentication |
| by itself does not trust the network or name servers or anything (but |
| the key); however, if somebody somehow steals the key, the key |
| permits an intruder to log in from anywhere in the world. This |
| additional option makes using a stolen key more difficult (name |
| servers and/or routers would have to be compromised in addition to |
| just the key). |
| .It Cm command="command" |
| Specifies that the command is executed whenever this key is used for |
| authentication. The command supplied by the user (if any) is ignored. |
| The command is run on a pty if the connection requests a pty; |
| otherwise it is run without a tty. A quote may be included in the |
| command by quoting it with a backslash. This option might be useful |
| to restrict certain RSA keys to perform just a specific operation. An |
| example might be a key that permits remote backups but nothing |
| else. Notice that the client may specify TCP/IP and/or X11 |
| forwardings unless they are explicitly prohibited. |
| .It Cm environment="NAME=value" |
| Specifies that the string is to be added to the environment when |
| logging in using this key. Environment variables set this way |
| override other default environment values. Multiple options of this |
| type are permitted. |
| .It Cm no-port-forwarding |
| Forbids TCP/IP forwarding when this key is used for authentication. |
| Any port forward requests by the client will return an error. This |
| might be used, e.g., in connection with the |
| .Cm command |
| option. |
| .It Cm no-X11-forwarding |
| Forbids X11 forwarding when this key is used for authentication. |
| Any X11 forward requests by the client will return an error. |
| .It Cm no-agent-forwarding |
| Forbids authentication agent forwarding when this key is used for |
| authentication. |
| .It Cm no-pty |
| Prevents tty allocation (a request to allocate a pty will fail). |
| .El |
| .Ss Examples |
| 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| .Pp |
| from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| .Pp |
| command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
| .Sh SSH_KNOWN_HOSTS FILE FORMAT |
| The |
| .Pa /etc/ssh/ssh_known_hosts |
| and |
| .Pa $HOME/.ssh/known_hosts |
| files contain host public keys for all known hosts. The global file should |
| be prepared by the admistrator (optional), and the per-user file is |
| maintained automatically: whenever the user connects an unknown host |
| its key is added to the per-user file. |
| .Pp |
| Each line in these files contains the following fields: hostnames, |
| bits, exponent, modulus, comment. The fields are separated by spaces. |
| .Pp |
| Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| wildcards); each pattern in turn is matched against the canonical host |
| name (when authenticating a client) or against the user-supplied |
| name (when authenticating a server). A pattern may also be preceded |
| by |
| .Ql ! |
| to indicate negation: if the host name matches a negated |
| pattern, it is not accepted (by that line) even if it matched another |
| pattern on the line. |
| .Pp |
| Bits, exponent, and modulus are taken directly from the host key; they |
| can be obtained, e.g., from |
| .Pa /etc/ssh/ssh_host_key.pub . |
| The optional comment field continues to the end of the line, and is not used. |
| .Pp |
| Lines starting with |
| .Ql # |
| and empty lines are ignored as comments. |
| .Pp |
| When performing host authentication, authentication is accepted if any |
| matching line has the proper key. It is thus permissible (but not |
| recommended) to have several lines or different host keys for the same |
| names. This will inevitably happen when short forms of host names |
| from different domains are put in the file. It is possible |
| that the files contain conflicting information; authentication is |
| accepted if valid information can be found from either file. |
| .Pp |
| Note that the lines in these files are typically hundreds of characters |
| long, and you definitely don't want to type in the host keys by hand. |
| Rather, generate them by a script |
| or by taking |
| .Pa /etc/ssh/ssh_host_key.pub |
| and adding the host names at the front. |
| .Ss Examples |
| closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| .Sh FILES |
| .Bl -tag -width Ds |
| .It Pa /etc/ssh/sshd_config |
| Contains configuration data for |
| .Nm sshd . |
| This file should be writable by root only, but it is recommended |
| (though not necessary) that it be world-readable. |
| .It Pa /etc/ssh/ssh_host_key |
| Contains the private part of the host key. |
| This file should only be owned by root, readable only by root, and not |
| accessible to others. |
| Note that |
| .Nm |
| does not start if this file is group/world-accessible. |
| .It Pa /etc/ssh/ssh_host_key.pub |
| Contains the public part of the host key. |
| This file should be world-readable but writable only by |
| root. Its contents should match the private part. This file is not |
| really used for anything; it is only provided for the convenience of |
| the user so its contents can be copied to known hosts files. |
| These two files are created using |
| .Xr ssh-keygen 1 . |
| .It Pa /var/run/sshd.pid |
| Contains the process ID of the |
| .Nm |
| listening for connections (if there are several daemons running |
| concurrently for different ports, this contains the pid of the one |
| started last). The contents of this file are not sensitive; it can be |
| world-readable. |
| .It Pa $HOME/.ssh/authorized_keys |
| Lists the RSA keys that can be used to log into the user's account. |
| This file must be readable by root (which may on some machines imply |
| it being world-readable if the user's home directory resides on an NFS |
| volume). It is recommended that it not be accessible by others. The |
| format of this file is described above. |
| .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
| These files are consulted when using rhosts with RSA host |
| authentication to check the public key of the host. The key must be |
| listed in one of these files to be accepted. |
| The client uses the same files |
| to verify that the remote host is the one we intended to |
| connect. These files should be writable only by root/the owner. |
| .Pa /etc/ssh/ssh_known_hosts |
| should be world-readable, and |
| .Pa $HOME/.ssh/known_hosts |
| can but need not be world-readable. |
| .It Pa /etc/nologin |
| If this file exists, |
| .Nm |
| refuses to let anyone except root log in. The contents of the file |
| are displayed to anyone trying to log in, and non-root connections are |
| refused. The file should be world-readable. |
| .It Pa /etc/hosts.allow, /etc/hosts.deny |
| If compiled with |
| .Sy LIBWRAP |
| support, tcp-wrappers access controls may be defined here as described in |
| .Xr hosts_access 5 . |
| .It Pa $HOME/.rhosts |
| This file contains host-username pairs, separated by a space, one per |
| line. The given user on the corresponding host is permitted to log in |
| without password. The same file is used by rlogind and rshd. |
| The file must |
| be writable only by the user; it is recommended that it not be |
| accessible by others. |
| .Pp |
| If is also possible to use netgroups in the file. Either host or user |
| name may be of the form +@groupname to specify all hosts or all users |
| in the group. |
| .It Pa $HOME/.shosts |
| For ssh, |
| this file is exactly the same as for |
| .Pa .rhosts . |
| However, this file is |
| not used by rlogin and rshd, so using this permits access using SSH only. |
| .Pa /etc/hosts.equiv |
| This file is used during |
| .Pa .rhosts |
| authentication. In the |
| simplest form, this file contains host names, one per line. Users on |
| those hosts are permitted to log in without a password, provided they |
| have the same user name on both machines. The host name may also be |
| followed by a user name; such users are permitted to log in as |
| .Em any |
| user on this machine (except root). Additionally, the syntax |
| .Dq +@group |
| can be used to specify netgroups. Negated entries start with |
| .Ql \&- . |
| .Pp |
| If the client host/user is successfully matched in this file, login is |
| automatically permitted provided the client and server user names are the |
| same. Additionally, successful RSA host authentication is normally |
| required. This file must be writable only by root; it is recommended |
| that it be world-readable. |
| .Pp |
| .Sy "Warning: It is almost never a good idea to use user names in" |
| .Pa hosts.equiv . |
| Beware that it really means that the named user(s) can log in as |
| .Em anybody , |
| which includes bin, daemon, adm, and other accounts that own critical |
| binaries and directories. Using a user name practically grants the |
| user root access. The only valid use for user names that I can think |
| of is in negative entries. |
| .Pp |
| Note that this warning also applies to rsh/rlogin. |
| .It Pa /etc/ssh/shosts.equiv |
| This is processed exactly as |
| .Pa /etc/hosts.equiv . |
| However, this file may be useful in environments that want to run both |
| rsh/rlogin and ssh. |
| .It Pa $HOME/.ssh/environment |
| This file is read into the environment at login (if it exists). It |
| can only contain empty lines, comment lines (that start with |
| .Ql # ) , |
| and assignment lines of the form name=value. The file should be writable |
| only by the user; it need not be readable by anyone else. |
| .It Pa $HOME/.ssh/rc |
| If this file exists, it is run with /bin/sh after reading the |
| environment files but before starting the user's shell or command. If |
| X11 spoofing is in use, this will receive the "proto cookie" pair in |
| standard input (and |
| .Ev DISPLAY |
| in environment). This must call |
| .Xr xauth 1 |
| in that case. |
| .Pp |
| The primary purpose of this file is to run any initialization routines |
| which may be needed before the user's home directory becomes |
| accessible; AFS is a particular example of such an environment. |
| .Pp |
| This file will probably contain some initialization code followed by |
| something similar to: "if read proto cookie; then echo add $DISPLAY |
| $proto $cookie | xauth -q -; fi". |
| .Pp |
| If this file does not exist, |
| .Pa /etc/ssh/sshrc |
| is run, and if that |
| does not exist either, xauth is used to store the cookie. |
| .Pp |
| This file should be writable only by the user, and need not be |
| readable by anyone else. |
| .It Pa /etc/ssh/sshrc |
| Like |
| .Pa $HOME/.ssh/rc . |
| This can be used to specify |
| machine-specific login-time initializations globally. This file |
| should be writable only by root, and should be world-readable. |
| .Sh AUTHOR |
| Tatu Ylonen <ylo@cs.hut.fi> |
| .Pp |
| Information about new releases, mailing lists, and other related |
| issues can be found from the SSH WWW home page: |
| .Pp |
| .Dl http://www.cs.hut.fi/ssh. |
| .Pp |
| OpenSSH |
| is a derivative of the original (free) ssh 1.2.12 release, but with bugs |
| removed and newer features re-added. Rapidly after the 1.2.12 release, |
| newer versions bore successively more restrictive licenses. This version |
| of OpenSSH |
| .Bl -bullet |
| .It |
| has all components of a restrictive nature (ie. patents, see |
| .Xr ssl 8 ) |
| directly removed from the source code; any licensed or patented components |
| are chosen from |
| external libraries. |
| .It |
| has been updated to support ssh protocol 1.5. |
| .It |
| contains added support for |
| .Xr kerberos 8 |
| authentication and ticket passing. |
| .It |
| supports one-time password authentication with |
| .Xr skey 1 . |
| .El |
| .Pp |
| The libraries described in |
| .Xr ssl 8 |
| are required for proper operation. |
| .Sh SEE ALSO |
| .Xr rlogin 1 , |
| .Xr rsh 1 , |
| .Xr scp 1 , |
| .Xr ssh 1 , |
| .Xr ssh-add 1 , |
| .Xr ssh-agent 1 , |
| .Xr ssh-keygen 1 , |
| .Xr ssl 8 |